1. Field of the Invention
The present invention relates to a semiconductor light emitting device including a light emitting element such as an LED (light emitting diode).
2. Description of the Related Art
Light emitting diodes (hereinafter called LEDs) are used in car tail lamps, various displays, the backlights of mobile devices such as mobile phones, and so on. The demand for LEDs for car headlights, the backlights of liquid crystal displays, and general lighting is expected to increase greatly from now on. For car headlights and general lighting, white light is desirable. The color of light of the LED is determined by the magnitude of the band gap of the semiconductor layer and is intrinsic to the semiconductor crystal used. Hence, the color of light of the LED is a single color such as red, green, or blue. The methods for obtaining white light using LEDs of this light-emitting characteristic are as follows.
The first method is to arrange a red LED, a green LED, and a blue LED and make them emit light at the same time. However, in the case of this method, color unevenness may be likely to occur depending on the viewing direction because of the strong directivity characteristic of LEDs. Further, because the rate at which the LED varies with an environmental factor such as temperature is different between the LEDs of respective different colors and the speed at which the LED deteriorates is also different, it is difficult to maintain the white color.
The second method is to combine a blue LED and a yellow fluorescent substance, thereby obtaining white light. The fluorescent substance absorbs blue light to emit yellow light of a longer wavelength. Part of blue light emitted from the blue LED is converted by the fluorescent substance into yellow light, and the other part passes through a fluorescent substance layer including the fluorescent substance with maintaining its blue color. The yellow light emitted from the fluorescent substance and the blue light are mixed to produce white light. According to this method, white light can be obtained with use of a single blue LED chip, and hence the device is simple in configuration and can be manufactured at lower cost than by the above first method wherein LEDs of emission colors of RGB are arranged.